[Xastir] Xastir and Ultimeter weather station

[Alex Carver]

--- Richard Polivka <r.polivka at sbcglobal.net> wrote:

> I agree on the -99999 selection since any other real
> value is possibly correct.
> 
> Gerry Creager <gerry.creager at tamu.edu> wrote:
> too! And you just raised a key one.  We should have
> a standard value for 
> *Missing Data* such as, -99999 (which is, in fact,
> one such well 
> recognized value in the meteorological community).

I see one sticky wicket for that in the consumer
equipment (now that I got to see the data format). 
Some of the units send unsigned integers for certain
values in their serial data stream.  They're also
using fixed width fields in the data stream.

For example, if the wind vane broke or didn't exist,
what value do you send for wind direction?  The
Ultimeter uses 0-F to send 16 directions of wind.  The
wind speed is encoded in two hex digits (no mention of
signed or unsigned here, though) so what do you send
there?  A report of 00 is valid as is 8A (140MPH not
often, but it might be valid in a hurricane).

If it's perhaps a simple firmware change that can be
installed in all existing units, maybe the no sensor
value should be an overrange.  Wind speed sensor
missing would be FF (unless there are 255 MPH winds
somewhere).

It looks like the temperature sensors might be get
away with a negative underrange, though, since they
have to transmit negative temperatures.  I can't tell
how they do it, though (whether signed integers or
some offset).




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